Child actor componoent deletes itself before the parent in endless runner?

i have been following this tutorial by unreal engine 4 to make an endless runner:

i followed the tutorial, made the rock to be spawned as the child actor component, so that it deletes itself when the actor deletes itself.
i ran into a problemr. after i made the obstacles, everythinw was working fine, the obstacles were spawning perfectly.

but the child actor component deletes itself, way before the actor! is it not attaching itself properly? is it not spawning properly? i tried to find out the problem, but since i am a little new, i couldnt find out what was wrong.

as you can see in the picture, the box deletes itself after that point before reacing to the player, and this distance grows in time.

here are the blueprints

please help me identify where i went wrong.